Indirectly heated cathode



Jan. 2, 1934. v JOBST 1,941,692

INDIRECTLY HEATED CATHODE Filed Sept. 26 1928 INVENTOR GUNT/IER. 70557 j2 ddauw AT NEY Patented Jan. 2, 1934 UNITED STATES PATENT OFFICEINDIRECTLY HEATED CATHODE Application September 26,

1928, Serial No.

308,403, and in Germany October 21, 1927 2 Claims.

The present invention is concerned with a new screen and 3 the heaterwire. 4 designates the thus distortions in reproduction.

Now, according to the present invention this inconvenience is obviatedby that the heater element is screened from the emitting surface orfilm. This is insured by that the resistor heated by the alternatingcurrent is wholly or partly surrounded by a tubular metallic screen,such as a metallic hose or grate in such a manner that the heater wireis shielded from the emitting cathode or filament layer and the otherelectrodes. In accordance with a modification the disturbing action ofthe alternating current is entirely elimi nated by virtue of the factthat the said protective hose is brought out of the tube and connectedto a definite potential, so that electrostatic coupling between theactive filament and the grid and the plate is avoided. Another schemewould be to bring both ends out of the tube and to compensate theharmful potential fluctuations by a convenient direct current oralternating current potential.

The manner in which this invention is carried out will be readilyunderstood from the following description taken in connection with theaccompanying drawing, which discloses one specific embodiment by way ofexample.

The single figure is a fragmentary diagrammatic view of a specificembodiment of this invention.

Referring to the drawing, 1 denotes the active coating of the cathode, 2the insulated protective metallic protector tube or metallic hose whichforms a continuation of the screen 2 at each end thereof according tothis invention, the metallic protector tubes being brought out of thetube, and containing the heater wire supply leads which are insulatedtherefrom by means of glass or quartz beads 5. 6 is a control grid whichis disposed spirally about the heater in well known manner.

It will be understood that many changes in the specific embodimentdisclosed herein will readily suggest themselves to those skilled in theart. For example, the coating 1 may be deposited directly upon the tube4. I therefore do not intend to be limited except as defined in theappended claims.

Having thus described my invention, I claim:

1. An indirectly heated cathode for an electron discharge device,comprising a rectilinear heater element, a tubular electron emittingmember surrounding and spaced from said heater element, a tubularmetallic screen interposed between said heater and said electronemitting member and separated from both the heater and the electronemitting member by vacuous space, and insulating means at each end ofthe tubular screen for maintaining said heater element in spacedrelation with respect to said tubular screen.

2. An indirectly heated cathode for an electron discharge device,comprising a heater element, a pair of lead-in conductors connected tothe heater terminals, a cathode sleeve substantially coextensive withand surrounding the heater, a tubular metallic screen interposed betweensaid heater and said cathode sleeve and separated from each by vacuousspace, said tubular metallic screen extending beyond the heaterterminals and separately enclosing each of the heater lead-inconductors.

GiiNTHER JOBST.

